Space enthusiasts have long dreamed of propelling spacecraft by sunlight. The idea of “solar sailing” goes back to astronomer Johannes Kepler, who wrote to Galileo in 1608 of “ships or sails adapted to the heavenly breezes.” More recently, in 1976, Carl Sagan went on the Tonight Show to propose a NASA sailing mission. It never happened. Until recently, in fact, nobody put together the money and resources to get a project into orbit.

Solar sailing happens when a spacecraft is pushed along by the force of solar radiation–that is, the momentum caused by billions of photons of light hitting a wide reflective surface. The test prototype now being built by the Planetary Society is composed of a box the size of a loaf of bread. In orbit, it’s designed to unfurl some solar panels to generate electricity (to power onboard components), and then launch 32-square-meter wings which provide the long-range propulsion.

A flight to test the basic mechanics is set for Wednesday, May 20. A more ambitious flight to test the actual “solar sailing” technology is scheduled for 2016. See more in the video here:

The project is fronted by Bill Nye (a.k.a. the “Science Guy”) who heads the Planetary Society. Some of the $5.45 million budget has come from a Kickstarter campaign. The CubeSat loaf will be pushed into space by a separate aircraft called Prox-1, which has been developed by graduates and undergraduates at Georgia Tech.